A lithium ion secondary battery is a type of secondary batteries that operates by the principle of generating a battery as lithium ions move between a cathode and an anode. Components of the lithium secondary battery may be broadly categorized as a cathode, an anode, a separator, and an electrolyte. A cathode active material and an anode active material among the components may have a structure, in which lithium in an ionic state may be intercalated into and deintercalated from the active materials, and charge and discharge may be performed by a reversible reaction.
Typically, lithium metal has been used as an anode active material of a lithium secondary battery. However, since there is a risk of explosion because a battery short circuit may occur due to the formation of dendrites when the lithium metal is used, a carbon-base material has been widely used as an anode active material instead of the lithium metal.
Examples of the carbon-based material may be crystalline carbon, such as graphite and artificial graphite, and amorphous carbon, such as soft carbon and hard carbon. The amorphous carbon may have high capacity, but irreversibility may be high during a charge and discharge process. Graphite is typically used as the crystalline carbon and has a high theoretical capacity limit. However, even through the crystalline carbon or the amorphous carbon has relatively high theoretical capacity, the theoretical capacity is only about 380 mAh/g. Thus, it may be difficult to use the crystalline carbon or the amorphous carbon as an anode during the development of a high capacity lithium battery.
Therefore, research into using lithium titanium oxide (LTO), spinel-structured metal oxide, as an anode active material has recently been actively conducted in order to develop a lithium ion secondary battery having battery performance, such as high speed charge and discharge and long lifetime.
Since the LTO does not generate a solid electrolyte interface (SEI) layer which is generated due to a secondary reaction between a graphite-based anode active material and an electrolyte that are now commonly used in a lithium ion secondary battery, the LTO may be excellent in terms of the occurrence of irreversible capacity in comparison to graphite and may have excellent reversibility for the intercalation and deintercalation of lithium ions even during repetitive charge and discharge cycles. Also, since the LTO has a relatively stable structure, it is a promising material that may manifest long lifetime performance of a secondary battery.
The LTO may be classified as two types, in which the LTO is only composed of primary particles and the LTO is composed of secondary particles that are formed by the agglomeration of the primary particles. In the case that the LTO is composed of the primary particles, adhesion to an electrode may not be problematic when the LTO has an appropriate particle diameter, but charge and discharge characteristics may degrade. Therefore, in the case in which the particle diameter of the prepared LTO is 300 nm or less in order to complement such shortcomings and improve high rate capability, limitations in a process during the preparation of a slurry may occur due to the increase in a specific surface area. Also, in the case that the secondary particles are formed in order to address the limitations of the nano-primary particles, improvement of the limitations may be obtained. However, a large amount of a binder may be required in order to maintain the adhesion to the electrode. Since the binder may act as an electrical resistive element of the electrode, a total energy density of the battery may be finally decreased.
In addition, in line with the improvement of the function of a device using a battery, a battery having a high energy density has been required. In order to satisfy this requirement, a technique that may increase energy per unit volume is required. In order to improve the energy per unit volume, a high-density electrode may be formed by increasing an amount of an electrode material to be coated per unit volume, and thus, a battery having high energy may be formed.
Therefore, an active material that may improve electrode density by decreasing the amount of the binder is required.